Remove NOTE(CONSTCOND) and note.h

These were mostly used to annotate do {} while(0)s

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Issue #12201

include/sys/dsl_dir.h

@@ -218,7 +218,7 @@ void dsl_dir_cancel_waiters(dsl_dir_t *dd);
 	dprintf("dd=%s " fmt, __ds_name, __VA_ARGS__); \
 	kmem_free(__ds_name, ZFS_MAX_DATASET_NAME_LEN); \
 	} \
-_NOTE(CONSTCOND) } while (0)
+} while (0)
 #else
 #define	dprintf_dd(dd, fmt, ...)
 #endif